Probe for pressure meter

ABSTRACT

The invention relates to a probe intended to be fitted to a pressure meter and including a fluid dispenser ( 1 ), a central measuring cell ( 21 ) suitable for being inflated by a pressurized liquid, and two boundary cells ( 22, 23 ) arranged on either side of the measuring cell and suitable for being inflated by a pressurized gas. According to the invention, the cells ( 21 - 23 ) are made from a single resilient sleeve ( 2 ) sheathing a hollow cylindrical mandrel ( 3 ) removably and sealingly fitted onto the dispenser ( 1 ), which dispenser has to this end an external surface in the shape a cylinder.

The invention concerns, in general terms, logging techniques.

More precisely, the invention concerns a probe for a pressure meter,comprising at least one fluid distributor and three inflatable annularcells, the distributor extending parallel to the axis of the probe andcomprising hydraulic fluid passages and gaseous fluid passages, and thecells extending respectively over three successive adjacent longitudinalsections of the probe, surrounding the distributor, and comprising acentral cell connected to at least one hydraulic fluid passage and twolateral cells, each of which is connected to at least one gaseous fluidpassage.

Pressure meters have been well known to persons skilled in the art sincetheir invention by L Ménard in 1955, and are used for evaluatingmechanical parameters of soils in situ.

Once the probe has been introduced into a borehole, each inflatable cellis subjected to a pressure increasing in stages, six to fourteen innumber for example, and in an arithmetic progression.

At each stage, the volume of liquid introduced into the central cell ismeasured at several instants after the end of the pressurisation.

These measurements are then translated into graphs from which themechanical parameters of the terrain explored are evaluated.

In practice, the volume measurements are therefore made only with thecentral cell, also referred to as the “measuring cell”, the lateralcells or “guard cells” merely having the function of confining thecentral cell in a substantially cylindrical volume in order to guaranteethat the results obtained do not depart from their field of validity.

The known probes, which constitute essential components of the existingpressure meters, suffer from several very annoying defects.

This is because these probes generally have a complex structure, so thatthey require long manufacturing times and high manufacturing costs.

Moreover, the intrinsic fragility of the elastic membranes used forproducing the cells and the relatively high frequency of damage thatresults from this, now lead to significant operating delayscorresponding to the time required for procuring a new probe.

In this context, the purpose of the present invention is to propose aprobe free from these main defects.

To this end, the probe of the invention, also in accordance with thegeneric definition given by the above preamble, is essentiallycharacterised in that the distributor has an external surface fittingwithin a cylinder, in that the probe also comprises a removable andsealed hollow cylindrical mandrel on the distributor and having at leastthree fluid orifices with a sealed separation from one another andopening out respectively in the three longitudinal sections of theprobe, the orifice of the central section being connected to at leastone hydraulic fluid passage and each of the other two orifices beingconnected to at least one gaseous fluid passage, and in that the threecells are at least partially formed by a single elastic sleeve fitted onthe mandrel and divided, by means of hoops locally applying and sealingthis sleeve so against the external face of the mandrel, in order toform the three longitudinal sections of the probe.

Not only can the probe thus arranged be produced easily and at lesscost, but it can also easily be repaired in the event of damage byreplacing the mandrel carrying the defective cells with a mandrelequipped with a new elastic sleeve.

The hoops comprise for example two end hoops, each of which consists ofa metal crimp, and two intermediate hoops, each of which consist of aplurality of turns of a flexible tie coiled under tension around thesleeve.

In order to more easily achieve a seal between cells and guarantee thedimensional stability of the cells, the mandrel can have two externalperipheral grooves, each intermediate hoop applying the elastic sleeveagainst the bottom of one of these grooves.

In a simple and effective embodiment of the probe of the invention, theturns of the flexible tie of each intermediate hoop are held withrespect to one another and under tension by adhesive bonding, forexample by means of a two-component adhesive.

The probe can also comprise a deformable protective mechanical sheath,for example produced from a coated textile.

In the case where such a protective sheath is used, the metal crimps areapplied to this sheath.

The probe of the invention is also provided with O-ring seals applied inexternal peripheral grooves of the distributor and isolating from oneanother with a seal, the three fluid orifices formed in the mandrel.

Other characteristics and advantages of the invention will emergeclearly from the description that is given below, by way of indicationand no way exhaustively, with reference to the accompanying drawings, inwhich:

FIG. 1 is a view in divided partial axial section of a probe accordingto the invention; and

FIG. 2 is a view in axial section, to an enlarged scale, of alongitudinal length of the probe illustrated in FIG. 1.

As stated previously, the invention concerns a probe intended to equip apressure meter.

Such a probe comprises, traditionally, a fluid distributor 1 and threeinflatable annular cells 21, 22 and 23.

The distributor 1 extends along the axis Z of the probe and compriseshydraulic fluid passages 11 and gaseous fluid passages 12.

The cells 21, 22 and 23 surround the distributor 1 and extendrespectively over three successive adjacent longitudinal sections of theprobe, denoted S1, S2 and S3.

The central measuring cell 21 is connected to a hydraulic fluid passage11, generally consisting of water under pressure, while the guard cells22 and 23, which are disposed on each side of the central cell 21, areeach connected to a gaseous fluid passage 12, this gaseous fluidgenerally consisting of pressurised nitrogen.

According to the invention, the cells 21 to 23 are produced from asingle elastic sleeve 2, sheathing a removable, sealed hollowcylindrical mandrel 3 on the distributor 1, this distributor for thispurpose having an external surface within a cylinder.

More precisely, the mandrel 3 has three fluid orifices sealed off fromone another, denoted 31, 32 and 33, and opening out respectively in thethree longitudinal sections S1, S2 and S3 of the probe.

The orifice 31 of the central section S1 is connected to the hydraulicpassage 11, and each of the orifices, 32 and 33, is connected to thegaseous fluid passage 12.

To define the three cells 21, 22 and 23 and form the corresponding threelongitudinal sections S1, S2 and S3 of the probe, the elastic sleeve 2is divided by means of hoops such as 4 e and 4 i that are locallyapplied and sealed off against the external face of the mandrel 3.

These hoops comprise in particular two end hoops 4 e each consisting ofa metal crimp.

In the case where the sleeve 2 is covered with a deformable protectivemechanical sheath 5, for example produced from a coated textile, themetal crimps 4 e are applied against this sheath 5.

The hoops comprise two intermediate hoops 4 i intended to provideseparation between the central cell 21 and the guard cells 22 and 23.

It should be stated here that, for reasons of size of representation,only the location of the hoops 4 i is made visible in FIG. 1.

As shown on the other hand in FIG. 2, each of the intermediate hoops 4 iis advantageously formed by a plurality of turns of a flexible tiecoiled under tension around the sleeve 2, these turns preferably beingheld with respect to one another and under tension by adhesive bonding.

To facilitate the placing and holding of the intermediate hoops 4 i, themandrel 3 preferably has two external peripheral grooves 30, eachintermediate hoop 4 i thus being able to apply the elastic sleeve 2against the bottom of one of these grooves 30.

Finally, as shown by FIG. 1, the probe of the invention is equipped withO-ring seals 6 installed in external peripheral grooves 10 of thedistributor 1 and sealed off to isolate from one another the three fluidorifices 31, 32 and 33 formed in the mandrel 3.

1. Probe for a pressure meter, comprising at least one fluid distributor(1) and three inflatable annular cells (21-23), the distributor (1)extending parallel to the axis (Z) of the probe and comprising hydraulicfluid passages (11) and gaseous fluid passages (12), and the cells(21-23) extending respectively over three successive adjacentlongitudinal sections (S1-S3) of the probe, surrounding the distributor(1), and comprising a central cell (21) connected to at least onehydraulic passage (11) and two lateral cells (22, 23), each of which isconnected to at least one gaseous fluid passage (12), characterised inthat the distributor (1) has an external surface fitting within acylinder, in that the probe also comprise a removable and sealed hollowcylindrical mandrel (3) fitted on the distributor (1) and having atleast three fluid orifices (31-33) sealed off to isolate from oneanother and opening out respectively in the three longitudinal sections(S1-S3) of the probe, the orifice (31) in the central section (S1) beingconnected to at least one hydraulic fluid passage (11) and each of theother two orifices (32, 33) being connected to at least one gaseousfluid passage (12), and in that the three cells (21-23) are at leastpartially formed by a single elastic sleeve (2) fitted on the mandrel(3) and divided, by means of hoops (4 e, 4 i) locally applying thissleeve (2) and sealed against the external face of the mandrel (3), inorder to form the three longitudinal sections (S1-S3) of the probe. 2.Probe according to claim 1, characterised in that the hoops (4 e, 4 i)comprise two end hoops (4 e), each of which consists of a metal crimp.3. Probe according to claim 1, characterised in that the hoops (4 e, 4i) comprises two intermediate hoops (4 i), each of which is formed by aplurality of turns of a flexible tie coiled under tension around thesleeve (2).
 4. Probe according to claim 3, characterised in that themandrel (3) has two external peripheral grooves (30) and in that eachintermediate hoop (4 i) applies the elastic sleeve (2) at the bottom ofone of these grooves (30).
 5. Probe according to claim 3, characterisedin that the turns of the flexible link of each intermediate hoop (4 i)are held with respect to one another and under tension by adhesivebonding.
 6. Probe according to claim 2, characterised in that it alsocomprises a deformable protective mechanical sheath (5), for exampleproduced from coated textile.
 7. Probe according to claim 6,characterised in that the metal crimps (4 e) are applied against theprotective mechanical sheath (5).
 8. Probe according to claim 1,characterised in that it comprises O-ring seals (6) applied in externalperipheral grooves (10) of the distributor (1) and sealed off to isolatefrom one another the three fluid orifices (31-33) formed in the mandrel(3).
 9. Probe according to claim 2, characterised in that the hoops (4e, 4 i) comprises two intermediate hoops (4 i), each of which is formedby a plurality of turns of a flexible tie coiled under tension aroundthe sleeve (2).
 10. Probe according to claim 1, characterised in that italso comprises a deformable protective mechanical sheath (5), forexample produced from coated textile.
 11. Probe according to claim 2,characterised in that it comprises O-ring seals (6) applied in externalperipheral grooves (10) of the distributor (1) and sealed off to isolatefrom one another the three fluid orifices (31-33) formed in the mandrel(3).